The M25 or London Orbital Motorway is a major road encircling almost all of Greater London. The 117-mile motorway is one of the most important roads in the UK and one of the busiest. Margaret Thatcher opened the final section in 1986, making the M25 the longest ring road in Europe. The Dartford Crossing closes the orbital route but is not classed as motorway; it is classed as a trunk road and designated as the A282. In some cases, such as the Communications Act 2003, the M25 is used as a de facto reference to Greater London.
